1. Field of the Invention
This invention relates to methods and systems for contact duplicating magnetic recordings such as those provided in magnetic recording disks, diskettes, and tapes and in particular to such methods and systems where anhysteretic contact duplication is effected.
2. Description of the Prior Art
Magnetic recording has traditionally been faced with the intrinsic inability of that recording concept to provide mass produced, inexpensive duplicates, such as are provided by stamped phonograph record replicas. In an attempt to at least approximate similar duplicates, various techniques for effecting the contact duplication of magnetic records have evolved. Generally, these techniques involve the common first step of placing a prerecorded master tape in surface contact with an unrecorded slave tape. In one approach, the contacted media are then heated to a temperature above the Curie temperature of the slave medium, but below the Curie temperature of the master medium, and the contacted media are then recooled while still in contact. In another approach more germane to the present invention, an AC bias magnetic field is applied to the contacted tapes to anhysteretically record on the slave medium the magnetic pattern previously recorded on the master medium.
As used above and throughout the present specification and claims, the expression "contacted media", and analogous varients thereof, refer to the master and slave media being in intimate surface contact, or in sufficiently close proximity that the local fields associated with a prerecorded pattern in the master medium are of sufficient intensity to contact duplicate the localized field patterns in the master medium onto the slave medium without appreciable divergence of the local field patterns and a resultant lowering of pattern resolution. For example, a thin polymeric web may be sandwiched between the "contacted media" and yet be within the subject definition. An excellent review of these techniques is presented in the article "Magnetic Tape Duplication by Contact Printing" by H. Sugaya and F. Kobayashi, Ann. N.Y. Acad. Sci., Vol. 189, pp. 214-238, Jan. 1972.
Magnetic recording media exhibiting exceptionally high uniaxial anisotropy are now becoming somewhat well known, at least in experimental form. Such media in particular may be provided by using magnetic materials possessing very high magnetocrystalline anisotropy. For example, Mr. R. E. Fayling, the present inventor has previously disclosed magnetic recording tapes made in a conventional manner using particulate barium ferrite and an organic binder, which tapes possess such uniaxial anistropy. See "Anisotropic Erasure and Demagnetization Characteristics of Recording Tapes Comprising Particles with Uniaxial Magnetocrystalline Anisotropy", IEEE Trans. on Mag., Vol. MAG-13, No. 5, pp. 1391-93 (Sept. 1977). In that article, the effect on erasure and demagnetization of such media resulting from the application of AC magnetic fields applied along both the easy axis of magnetization and along the hard axis was reported, it being noted that such tapes were more resistant to erasure or demagnetization when the fields were applied along the hard axis.